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Escherichia coli adenylate cyclase homepage: Comments Warning This page is under reorganization following the removal of comments from PubMed Commons.  Your patience is greatly appreciated!

Nat Commun. 2017
Enzyme I facilitates reverse flux from pyruvate to phosphoenolpyruvate in Escherichia coli
Long CP, Au J, Sandoval NR, Gebreselassie NA, Antoniewicz MR

All data in this paper should be discarded simply because the strains used by the authors are not what the authors think they are, as explained below.

An Escherichia coli strain lacking PEP synthase does not grow on pyruvate.  In fact, the crucial role of PEP synthase during growth on pyruvate is well documented.  In brief, mutant strains were isolated which could grow on glucose or acetate but not on pyruvate; it was found they lacked PEP synthase (see Cooper RA, 1967 for an early paper).  Furthermore, because the PEP synthase gene (ppsA) is transcriptionally positively regulated by the fructose repressor FruR (Geerse RH, 1986, also known as Cra), fruR mutant strains are routinely checked for their inability to grow on pyruvate.  Therefore, data in supplementary Fig. 1 indicating wild type and ppsA strains grow equally well on pyruvate are incorrect; the strain used by the authors is not a ppsA strain.

The ptsI strain also does not appear to be a ptsI strain, as it grows on xylose as well as a wild type strain (figure 3b), it should not; growth on xylose requires cAMP, which requires the phosphorylated form of Enzyme IIAGlc.

Sci Rep. 2016
The lag-phase during diauxic growth is a trade-off between fast adaptation and high growth rate
Chu D, Barnes DJ

It is astounding that the authors totally ignore the specific effects of cAMP on the lag phase of the glucose-lactose diauxie.  Not only does addition of cAMP eliminate the diauxic lag, it also clearly impairs growth on glucose (see figure 1 in Ullmann A, 1968).  An increased level of cAMP triggers a 'leaky' expression of CRP-cAMP-dependent genes and operons (including the lactose operon) thereby affecting growth on glucose.  Leaky expression of genes reduces fitness in glucose, with a trade-off for a shorter diauxic lag (or, as in figure 1 mentioned above, a complete elimination of the lag phase resulting in biphasic growth).  In the Escherichi coli glucose-lactose diauxie, there is a correlation between the cAMP level and the cost-benefit trade-off.

J Bacteriol. 2015
Acetate Exposure Determines the Diauxic Behavior of Escherichia coli during the Glucose-Acetate Transition
Enjalbert B, Cocaign-Bousquet M, Portais JC, Letisse F

Growth of Escherichia coli on excess glucose under aerobic conditions was never reported to be diauxic, and the acetate switch was never "classically described as a diauxie".  It is therefore extraordinary that the authors are now showing that "diauxic behavior does not occur under such conditions".  A diauxie in the presence of both glucose and acetate in the culture medium was reported by Kao KC, 2005.

Sci Rep. 2016
Glucose becomes one of the worst carbon sources for E. coli on poor nitrogen sources due to suboptimal levels of cAMP
Bren A, Park JO, Towbin BD, Dekel E, Rabinowitz JD, Alon U

There are several discrepancies in this paper which cannot be reconciled.  For example, Figure 1a and Table S1 indicate a growth rate of 0.76 hr-1 for maltotriose with ammonia as nitrogen source. The glucose-maltotriose diauxie with ammonia (Figure 2a, upper and middle panel) indicates a growth rate for maltotriose of 0.37 hr-1.  In diauxie, the growth rate on each sugar is characteristic of that sugar (Monod, 1942).  Therefore, the glucose-maltotriose diauxie should exhibit a growth rate of 0.76 hr-1 for maltotriose.  It is likely that the presence of the reporter gene in the diauxie experiment (Figure 2) is affecting the growth rate on maltotriose.

J Bacteriol. 2016
Classic Spotlight: When Phenotypic Heterogeneity Met Carbon Catabolite Repression
Becker A

Escherichia coli cells, when 'pre-induced' in the presence of the artificial inducer TMG, synthesize β-galactosidase in the presence of glucose.  COHN M, 1959 stated: "The effect of pre-induction is to restore in the presence of 10-3 M glucose about 50 per cent of the maximal differential rate obtainable on succinate".  The observation the maximal rate was not reached in the presence of glucose led the authors to argue, indeed incorrectly, that glucose was a preferential metabolic source for yielding high internal levels of repressor.  Such observation however will have an explanation later on with the discovery of the 'cAMP effect' on β-galactosidase synthesis, in agreement with the finding by COHN M, 1959 that carbon sources presently known to elicit higher cAMP levels (particularly succinate, lactate and glycerol, see Epstein W, 1975) were found to be non-inhibitory (i.e. allowing maximal differential rate).  Anke Becker’s final statement, that inhibition of lactose permease by unphosphorylated Enzyme IIA (leading to inducer exclusion) is primarily responsible for CCR of the lac operon, is therefore inappropriate as cAMP via its receptor protein (simultaneously designated as CRP by Emmer M, 1970 and CAP by Zubay G, 1970) also plays a role in CCR of the lac operon.  Furthermore, Jacques Monod (1942) reported diauxie was attenuated - but not eliminated - when the cells were pre-induced (adapted to the less preferred 'B' sugar).  Diauxie was however eliminated by addition of exogenous cAMP (Ullmann A, 1968).  Therefore, inducer exclusion and the level of cAMP both contribute to CCR of the lac operon.

Lastly, unphosphorylated EIIAGlc does not inhibit adenylate cyclase.  The current model of regulation postulates dephosphorylation of Enzyme IIA during glucose transport interferes with the activation of adenylate cyclase by phosphorylated Enzyme IIAGlc.

Microbiol Mol Biol Rev. 2015
The Emergence of 2-Oxoglutarate as a Master Regulator Metabolite
Huergo LF, Dixon R

Figure 7 is improperly done and rife with error.  One of the characteristic of the PTS is that its substrates are transported and phosphorylated concomitantly.  Therefore glucose phosphorylation does not occur inside the cell as depicted in Figure 7.  Representation of the phosphorylation state of the PTS proteins is misleading (a pale P for Enzyme IIAGlc does not lead to a dark P for Enzyme IICBGlc).

Furthermore, legend for Figure 7 wrongly indicates excess glucose increases the level of 2-oxoglutarate thereby inhibiting the phosphorylation cascade.  In fact, 2-oxoglutarate, which accumulates in nitrogen limitation, inhibits the PTS phosphorylation cascade (Doucette CD, 2011).  On the other hand, an increase in nitrogen availability (Figure 7C) causes an increase in glucose uptake, which cannot possibly activate adenylate cyclase to allow for transport of alternative carbon sources (in these conditions, glucose transport also prevents utilization of alternative carbon sources due to inducer exclusion).  Thus, in the presence of glucose, a decrease in 2-oxoglutarate upon sudden nitrogen availability is unlikely to 'partially activate adenylate cyclase' and 'activate carbon catabolite pathways', as stated.

A direct inhibition of adenylate cyclase by 2-oxoglutarate, as depicted in Figure 7B, relies on questionable studies (You C, 2013), and is not supported by data from Yang JK, 1983 (Table VII, caption a) indicating 10 mM 2-oxoglutarate (α-ketoglutarate) did not inhibit adenylate cyclase activity. 

Infect Immun. 2015
A genome wide screen reveals that Vibrio cholerae phosphoenolpyruvate phosphotransferase system (PTS) modulates virulence gene expression
Wang Q, Millet YA, Chao MC, Sasabe J, Davis BM, Waldor MK

Gene identification number VC1822 and VCA1045 relate to PTS proteins with A, B, and C domain (not just an A domain as inferred from the text).  In accordance with the 'Proposed Uniform Nomenclature' for the PTS proteins (Saier MH Jr, 1992), gene VC1822 encodes an Enzyme IIACBN/D and VCA1045 an Enzyme IICBAMtl.  It would be a great benefit for PTS researchers if the nomenclature was used beyond for example Escherichia coli.

Based on figure 6A, the authors report the CRP-cAMP complex negatively regulates the expression of tcpA in the absence of the PTS.  However, because figure 6A shows there is no significant difference in expression between the cya and the cya ptsH mutant strain or the crp and the crp ptsI mutant strain, and no significant difference in expression between the wild type and the crp or cya mutant strain, it could be concluded from figure 6A that the CRP-cAMP complex does not play a major role in the transcription of tcpA in the TCP-producing AKI medium used by the authors.  This conclusion is not supported by previous data indicating CRP-cAMP indirectly regulates negatively the expression of tcpA by inhibiting the transcription of tcpPH (Kovacikova G, 2001).  However the cAMP level varies in response to changes in carbon and energy sources.  Thus, if the level of cAMP is relatively low in the AKI medium as compared to LB medium, production of TcpA occurs. This provides an explanation for the present observation indicating deletion of crp does not significantly affect production of TcpA (figure 6A).  It also provides an explanation why incorporation of a crp mutation in the El Tor strain C6706 allows production of TCP in LB medium (Skorupski K, 1997).

Figure 6B does not indicate that "…in the EI or Hpr mutants, intracellular cAMP concentrations were significantly higher than that in wt cells" - as stated.  In fact, intracellular cAMP concentrations are significantly higher in the cpdA mutant strains, possibly indicating a role for cAMP phosphodiesterase in regulating the cAMP levels.

Mol Syst Biol. 2015
A growth-rate composition formula for the growth of E. coli on co-utilized carbon substrates
Hermsen R, Okano H, You C, Werner N, Hwa T

A diauxie was observed for the pair glucose-succinate (Lazzarini RA, 1971) therefore glucose and succinate most likely are not used simultaneously.  Thus in keeping with the questionable reasoning by the authors, the growth rate on the glucose-succinate pair (Table 1) should not be higher than the growth rate on either glucose or succinate.  The physiological relevance of the preceding article by You C, 2013, on which this report is based, is commented on below.

June 14, 2014
The Bacterial Phosphoenolpyruvate:Carbohydrate Phosphotransferase System: Regulation by Protein Phosphorylation and Phosphorylation-Dependent Protein-Protein Interactions.
Deutscher J, Aké FM, Derkaoui M, Zébré AC, Cao TN, Bouraoui H, Kentache T, Mokhtari A, Milohanic E, Joyet P

The authors stated: "cAMP formation seems to affect the lag phase" and "addition of extracellular cAMP either shortens or entirely eliminates the lag phase".  In fact addition of cAMP does not always eliminate the lag phase, for example the glucose-galactose diauxie.

The authors also stated: "addition of extracellular cAMP cannot prevent CCR [Carbon Catabolite Repression]".  Of course not, as generally the cAMP-regulated transcription and inducer exclusion both contributes to CCR.  However the extent of these effects depends on the system considered.  Thus elimination of inducer exclusion cannot prevent CCR as well, as best exemplified by CCR of the glycerol regulon.  (Note: the reference to support the contention that exogenous cAMP cannot prevent CRR is not appropriate, the strain used in the referenced article expresses β-galactosidase constitutively).  Finally the contention that inducer exclusion is the major CCR mechanism in E. coli is based on a flawed paper by Inada et al. (Diauxie correspondence)

The regulation of adenylate cyclase by phosphorylated Enzyme IIAGlc is poorly addressed as seen by the first reference to a paper by Krin et al.  That paper addresses the role of the histone-like protein H-NS on the cAMP levels, and its main conclusion is adenylate cyclase is not fully activated in a crp hns double mutant strain (lacking both CRP and H-NS) due to a reduced expression of crr which encodes EnzymeIIAGlc (a conclusion to be taken with caution considering the more than two-fold decrease in expression of the adenylate cyclase gene in the double mutant).  The statement that "low intracellular levels of cAMP are observed in E. coli cells grown on an efficiently metabolized carbon source" is erroneous, for example it does not apply to the PTS sugar fructose.  Also the contention that all PTS carbohydrates (one exception noted) are phosphorylated during their transport  might not be quite correct because certain sugars can be transported by facilitated diffusion without phosphorylation under specific conditions.

This review being released for the 50th anniversary of the PTS discovery by Kundig, Ghosh and Roseman, is disconcerting in that the pioneer's contributions was so poorly acknowledged.  In Conclusion and Perspectives, the authors stated: "The PTS was discovered 50 years ago in the laboratory of Saul Roseman at the University of Michigan, Ann Arbor, with the first article describing a PTS component, the HPr from E. coli, and its role in hexose phosphorylation being published in 1964".  In fact, the first article by Kundig, Ghosh and Roseman, besides characterizing the protein-bound phosphohistidine, remarkably indicated PEP (phosphoenolpyruvate) could act as the initial phosphoryl donor for their purified PTS proteins, D-sugars were PTS substrates and the product formed from glucose was glucose 6-phophate, and more than one Enzyme II could be synthesized by the cell.  Thus the landmark paper by Kundig, Ghosh and Roseman deserves recognition and should have been introduced with proper accolades.

Nature, 2013
Coordination of bacterial proteome with metabolism by cyclic AMP signalling
You C, Okano H, Hui S, Zhang Z, Kim M, Gunderson CW, Wang YP, Lenz P, Yan D, Hwa T

In an article by Doucette CD, 2011, it is clearly demonstrated that the effect of α-ketoglutarate on cAMP synthesis is related to an inhibition of Enzyme I.  As a consequence phosphorylation of Enzyme IIAGlc is impaired which relates to a decrease in cAMP synthesis, and yet You et al. studied the effect of α-ketoglutarate in pts mutant strains.  Because "a strong transient repression was still observed upon the addition of α-ketoacids in strains with deletion of various PTS proteins" - as stated - You et al. basically conclude that the PTS proteins are no longer necessary for mediating the main effect by α-ketoglutarate but instead α-ketoglutarate directly affect the activity of adenylate cyclase.  Incidentally 10 mM α-ketoglutarate does not inhibit purified adenylate cyclase.

The feedback strategy established by Doucette CD, 2011 relates to data obtained under conditions of 'extreme' catabolite repression elicited by nitrogen limitation.  A direct inhibitory effect of α-ketoglutarate on Enzyme I inhibits phosphorylation of the components of the phosphotransferase system (PTS), including phosphorylation of EnzymeIIAGlc which activates adenylate cyclase.  Therefore, cAMP-mediated catabolite repression occurs in these conditions.  Another not-yet propounded effect of an increase in α-ketoglutarate is an enhanced inducer exclusion, which further hinders uptake of carbon sources other than PTS substrates.  Under nitrogen-limited conditions, β-galactosidase synthesis in a wild-type strain growing on glucose is most likely affected by inducer exclusion.  Thus, nitrogen-limited growth may not 'rely completely' on cAMP-mediated gene regulation as transcriptional regulation by cAMP and inducer exclusion both interfere with β-galactosidase synthesis (Crasnier-Mednansky M, 2008).  By not taking into account inducer exclusion the authors undermine the power of 'quantitative physiology'.  Within the same frame of thought, using pts strains grown on lactose to measure β-galactosidase activity is physiologically irrelevant.

In sharp contrast with the present data, Daniel J, 1986 reported that α-ketoglutarate (or pyruvate indirectly by accumulation of α-ketoglutarate) caused repression of the lac operon - but not oxaloacetate.  In addition repression did not occur in crr strains (lacking Enzyme IIAGlc) in support of Doucette CD, 2011.

Be happy to know that "harsher treatment" - as stated - "may damage proteins" but "the results are meant to provide an alternative perspective"!  And the authors laughingly conclude: "Thus, the repression effect of α-ketoacids on AC [adenylate cyclase] activity is robust even in this harsh assay condition."  One may wonder, if using "harsh assay condition" does not make any difference, then the effect of α-ketoacids on AC activity seems to be quite questionable.  Next time the authors should try to boil their sample for a good amount of time, just to provide an 'alternative' control!

Nucleic Acids Res 2013
A genome-wide screen for identifying all regulators of a target gene
Baptist G, Pinel C, Ranquet C, Izard J, Ropers D, de Jong H, Geiselmann J

A ptsI mutant strain of Escherichia coli does not grow on minimal medium glucose after 48 hours.  Therefore the ptsI mutant strain from the Keio collection which is reported to grow on glucose with growth defect (see Supplementary Information, S3 and S7) is not adequate.  Therefore it is irrelevant to state "… the cyaA and crr mutants should behave as the ptsI strain" (see Section Confirmation of known regulators of acs expression) because, unlike ptsI strain, cyaA and crr mutant strains grow on glucose, even though they do not grow as well as a wild type strain (note it is also reported in S3 that gltA and icd mutant strains do not grow on glucose but they actually do when supplemented with glutamate).  In addition under the experimental conditions described, it is not clear to which extent glucose is used preferentially over acetate by certain mutant strains particularly in the presence of cAMP (absorbance should have been provided in Figure 4C, D, E and F).  Also the authors seem to ignore that any mutant strains lacking any of the TCA cycle enzymes fail to grow on acetate as they wrote "Interestingly we found that the above mutants [sucB and lpdA] fail to grow on acetate."

Researchers are better off reading the 2002 paper by James C. Liao and colleagues titled "Global expression profiling of acetate-grown Escherichia coli" which investigates the transcript profile of an E. coli strain grown on acetate as compared to the profile of the same strain grown on glucose (surprisingly none of the Liao papers are cited by the authors).

Finally, and most importantly, the authors should re-consider analyzing "connections between the metabolic state of the cell and gene expression" by using luciferase as a reporter system considering that luciferase strongly depletes the pool of cellular ATP.  No wonder mutant strains lacking genes involved in energy supply display the lowest luciferase activity!  And yet the authors used a second reporter system to detect "artifacts due to metabolic influences on luciferase activity", as stated in the Introduction.

April 27, 2013
Glucose Triggers ATP Secretion from Bacteria in a Growth-Phase-Dependent Manner
Hironaka I, Iwase T, Sugimoto S, Okuda K, Tajima A, Yanaga K, Mizunoe Y

The authors "assumed that enterococcal species and bacteria belonging to other genera might secrete ATP during growth" (sic), and claimed glucose is essential for ATP secretion.  However it is not clear what the glucose concentration used by the authors was in some of their experiments, particularly Figure 7.  Readers of this article may 'assume' the glucose concentration used in the culture medium of Escherichia coli MC4100 was not too high (so to speak) considering the growth curve presented in Figure 7.  Indeed figure 7 indicates an OD600 of about 0.5 was finally reached after a whopping 10 hours in an unspecified medium.  LB medium was used in their studies - as stated in Materials and Methods - and therefore one may presume it was used for Escherichia coli but there is no way of knowing, really.  And why was ATP detected in RPMI medium in Figure 2A and not in Figure 2C?  Possibly in Figure 2C the authors 'deleted' glucose from the RPMI medium, we may think!

January 24, 2013
Structures of the Escherichia coli transcription activator and regulator of diauxie, XylR: an AraC DNA-binding family member with a LacI/GalR ligand-binding domain
Ni L, Tonthat NK, Chinnam N, Schumacher

Introduction states: "With the broader goal of generating an E. coli biocatalyst that can co-metabolize all biomass sugars, it would be necessary to also eliminate the diauxie between D-xylose and L-arabinose, as these two sugars comprise 95% of the total sugar hemicellulose (6,7)."  Xylose and arabinose are two class B sugars for E. coli, as defined by Jacques Monod, and there is no report of a diauxic growth between xylose and arabinose even though E. coli was reported to preferentially utilize arabinose when grown in a mixture of xylose and arabinose.  Reference 6 reports that, in the presence of glucose, xylose and arabinose were simultaneously consumed in E. coli mutants impaired in Carbon Catabolite Repression (CCR), and reference 7, which suffers many flaws, is irrelevant to E. coli utilization of xylose and arabinose.

September 20, 2012
Corrigendum: Phosphoenolpyruvate phosphotransferase system regulates detection and processing of the quorum sensing signal autoinducer-2
Pereira CS, Santos AJM, Bejerano-Sagie M, Correia PB, Marques JC, Xavier KB

The corrigendum to the article (commented on below June 01, 2012) brings a corrected reference [Xavier et al., 1996, J Bacteriol] in support of the contention that "trehalose is one of the most abundant carbohydrates in LB media".  The 1996 article by Xavier et al. does not however establish that trehalose is the 'most abundant' sugar in LB medium but establishes the presence of trehalose in yeast extract (the presence of other sugars in yeast extract was not analyzed) therefore the trehalose permease may not be one of the "most induced" PTS permease in LB medium - as stated in their article.  Furthermore, indicating that trehalose is the most abundant sugar in LB medium is misleading considering the carbon sources for E. coli in LB medium are catabolizable amino acids, not sugars [J Bacteriol].  The presence of trehalose in yeast extract solely indicates that, in LB medium, intracellular trehalose-6-phosphate, which results from the transport of trehalose by the phosphotransferase system, may act as an inducer under certain experimental conditions.

June 01, 2012
Phosphoenolpyruvate phosphotransferase system regulates detection and processing of the quorum sensing signal autoinducer-2
Pereira CS, Santos AJM, Bejerano-Sagie M, Correia PB, Marques JC, Xavier KB

Transcription of the lsrACDBFGE operon, which encodes a quorum sensing signal autoinducer-2 (AI-2) uptake and modification system, is positively regulated by CRP-cAMP.  The flanking lsrRK operon encoding the repressor LsrR and AI-2 kinase is regulated as well by CRP-cAMP.  Also, uptake of AI-2 occurs during entry into stationary phase (referred to as '4 hours post inoculation' by the authors) which is known to be related to a rise in cAMP.  However by using a cya crp* strain (supposedly insensitive to catabolite repression) to "avoid selecting mutants affected in lsr-lacZ regulation due to altered cAMP levels" the authors circumvent addressing the regulatory effects of CRP-cAMP which are most likely controlling AI-2 uptake and modification.  It is therefore not surprising that they conclude, in view of their unsuccessful attempts to explain their observations, that "the mechanism enabling PTS-dependent AI-2 uptake remains unknown".  Furthermore Pereira et al. apparently ignore cAMP regulations linked to catabolite repression are not fully 'restored' in the pts mutants they isolated, particularly because the typical increase in cAMP observed in stationary phase does not occur in such mutants.  So much for avoiding the selection of mutants affected in lsr-lacZ regulation due to altered cAMP levels!

All isolated mutants have growth defects, but as stated, "… these [growth defects] are insufficient to explain the strong phenotypes observed with respect to AI-2 internalization observed" and in the same sentence "but can explain the slight delay in AI-2 accumulation when compared with the lsrK mutant strain"!  And, even better, because "AI-2 internalization observed in a EI mutant cannot be exclusively explained by the loss of any single permease" the authors conclude "multiple permeases, regulated by the PTS, contribute additively to the transport of AI-2".  And if you want to know what the PTS is you’ll find out that it provides a mechanism for 'intracellular sequestration' of the so-called PTS-sugars.  Who said 'Research is what I'm doing when I don't know what I'm doing'?

Appl Microbiol Biotechnol. 2012
A dodecapeptide (YQVTQSKVMSHR) exhibits antibacterial effect and induces cell aggregation in Escherichia coli
Lin KC, Chen CY, Chang CW, Huang KJ, Lin SP, Lin SH, Chang DK, Lin MR, Shiuan D

Escherichia coli strain DH5α grows very poorly in minimal media (Jung SC, 2010).  It is therefore inappropriate to use this strain "to determine the effect of selected peptides on bacterial cell growth", as stated.  In addition the contention by the authors that "binding of [the dodecapeptide] AP1 with HPr may block phosphotransfer and further phosphorylated enzymeIIA, thereby activate adenylate cyclase" is erroneous.  Blocking the phosphotransfer cannot result in adenylate cyclase activation.  And how a peptide which inhibits "the growth of Escherichia coli cells efficiently" can induce cell aggregation in the conditions described by the authors?

J Bacteriol. 2011
Novel Members of the Cra Regulon Involved in Carbon Metabolism in Escherichia coli
Shimada T, Yamamoto K, Ishihama A

Introduction section reads: "The induction of the fructose operon takes place when the repressor Cra [FruR] is inactivated after interactions with inducers such as D-fructose-1-phosphate and D-fructose-1, 6-biphosphate. … In the presence of glucose, the intracellular concentration of the inducers increase, which interact with Cra [FruR] to prevent its binding to the target promoters".  The intracellular concentration of the inducer fructose-1-phosphate does not increase in the presence of glucose.  It 'increases' in the presence of fructose which enters the cell as fructose-1-phosphate via the phosphotransferase system (PTS).  Furthermore the synthesis of 1-phosphofructokinase is specifically induced by fructose, and inhibited by fructose-1, 6-biphosphate.  Therefore in the presence of glucose (or mannose or mannitol) the intracellular concentration of the inducer fructose-1-phosphate cannot possibly 'increase'.  It increases in the presence of fructose.

J Bacteriol. 2011
This article was retracted in 2015

Escherichia coli exports cyclic AMP via TolC
Hantke K, Winkler K, Schultz JE

Results section reads: "Mutants like BTH2 cya grow as colorless colonies [on MacConkey agar plates].  Application of cAMP via filter paper discs resulted in a narrow red growth zone only around the disc which was soaked with 40 mM cAMP indicating cAMP dependent utilization of maltose" and same section further on: "Next, induction of β-galactosidase was assayed as a function of cAMP concentration.  The parent strain BTH2 cya was rather insensitive to cAMP addition.  Even at 10 mM cAMP in the medium a full response was not elicited indicating the presence of a highly effective system for cAMP export from the cells".  Both data indicates the BTH2 cya strain is unlike any other cya strains of E. coli.  Therefore the conclusion that E. coli exports cAMP via TolC must be taken with caution.

FEBS Lett. 2010
A mammalian insulysin homolog is regulated by enzyme IIA(Glc) of the glucose transport system in Vibrio vulnificus
Kim YJ, Ryu Y, Koo BM, Lee NY, Chun SJ, Park SJ, Lee KH, Seok YJ

Glucose does not trigger dephosphorylation of Enzyme IIAGlc in absence of the glucose permease (Enzyme IICBGlc).  Therefore glucose does not ensure complete dephosphorylation of Enzyme IIAGlc in the experimental conditions described by the authors in four instances.  (1) Material and Methods section reads: "To test the phosphorylation dependence of the interaction between IIAGlc and the vIDE, vIDE [V. vulnificus insulin-degrading enzyme] was incubated with EI, HPr and His-IIAGlc in a total volume of 500 µl of buffer A containing 2 mM DTT and 2 mM MgCl2 in the presence of 1 mM glucose (to ensure complete dephosphorylation of His-IIAGlc)…"  (2) Results section reads: "In one set of reactions, glucose was added, along with E. coli EI and HPr, to maintain IIAGlc in dephosphorylated form" and (3) same section further on: "To confirm whether IIAGlc is required for activity of vIDE, and to test whether this activation depends on the phosphorylation state of IIAGlc, the reaction mixture containing vIDE, EI, HPr and IIAGlc was pre-incubated with either PEP or glucose before the reaction was initiated by the addition of insulin"  (4) Legend of Figure 1(B) reads: "vIDE was incubated with EI and HPr in the presence or absence of His-IIAGlc.  Mixtures designated Glc and PEP were supplemented with 1 mM glucose and PEP to ensure complete dephosphorylation and phosphorylation of the added IIAGlc, respectively" (idem Figure 4).

J Bacteriol. 2009
Pyruvate kinase-deficient Escherichia coli exhibits increased plasmid copy number and cyclic AMP levels
Cunningham DS, Liu Z, Domagalski N, Koepsel RR, Ataai MM, Domach MM

Discussion reads: 'Prior work also indicated that PL8UV5 is about fourfold stronger than Plac when both are compared for growth on glucose (21)'.  Reference (21) does indeed describe lac up-promoter mutants including PUV5 but none of the mutants carry the L8 mutation.  And in a repeat performance: 'As a second control, Plac in PB25 was mutated to PL8UV5, which is cAMP insensitive and about fourfold stronger than Plac when these two promoters are compared for growth on either glucose-6-phosphate (37) or glucose (21)'.  In yet another example of citation violation, Discussion reads: '… glucose- 6-phosphate … is similar to glucose in repressive strength (29)'.  Not quite, see Table 1 in Reference (29).

J Bacteriol. 2009
Involvement of the Cra global regulatory protein in the expression of the iscRSUA operon, revealed during studies of tricarballylate catabolism in Salmonella enterica
Lewis JA, Boyd JM, Downs DM, Escalante-Semerena JC

Material and Methods section reads: 'Skovran et al. previously reported that an isc mutant required nicotinic acid and thiamine for growth. The requirements for these nutrients were bypassed by using overnight cultures grown in LB, without washing the cells, to inoculate fresh medium'.  This is incorrect experimental procedure which leads to false data.

Nat Rev Microbiol. 2009
cAMP does not have an important role in carbon catabolite repression of the Escherichia coli lac operon
Narang A

Wanner BL, 1978 stated "Much of the variation [in β-galactosidase synthesis] was eliminated by growing E. coli in the presence of cAMP, and this component we call cAMP-mediated catabolite repression".  The remaining repression [in the presence of cAMP] was carbon source dependent and growth related, and possibly mediated by cAMP, as concluded by the authors.  It is therefore extraordinary to read cAMP does not have an important role in carbon catabolite repression of the Escherichia coli lac operon.  In addition, this correspondence fully ignores the reasoning of a previous correspondence (Crasnier-Mednansky M, 2008) indicating a crucial role for cAMP in the glucose-lactose diauxie.

 Wanner BL, 1978 further indicated a large variation in β-galactosidase activity occurred in media supporting similar growth rate (thus synthesis rate is not constant).  Therefore their data did not indicate "β-galactosidase activity is inversely proportional to the specific growth rate", as reported in this correspondence.

In addition, data from Wanner BL, 1978 Figure 2B did not indicate addition of exogenous cAMP increased β- galactosidase activities less than two-fold.  In fact, media in which there was marked growth rate inhibition by cAMP also showed large stimulation of β-galactosidase synthesis, and a growth rate inhibition was not a necessary condition for an increase in the enzyme activity.